Lubricants and functional fluids used in submarine propulsion systems must meet challenging operating conditions. Submarines function very independently which means that their operating systems need to perform reliably over long time periods. If a problem occurs with a submarine at sea, the chances for outside assistance are remote. A lubricating fluid in a submarine must therefore be very reliable and due to weight restraints multifunctional.
The current lubricating oil used in submarines (known as 2190-TEP) is a mineral oil based fluid that meets the military specification MIL-PRF-17331. This oil has been used in submarines for the past forty years but the US Navy has increased the severity of the operating conditions in its fleet.
One of the principal objectives of the present invention is to provide lubricating oil that can provide effective lubricity to faster new drive systems that have much higher gear-to-fluid volume interactions, while under higher operating temperatures, which lead to more thermal efficiency. The net result of these more stressful operating conditions is that the existing fluid is failing more quickly leading to high oil replacement and high disposal costs.
The three problems associated with this general objective are (a) high depletion of antioxidants in the mineral oil based fluid, (b) sharp increases in total acid number and (c) severe off-gassing events. Degradation leads to the formation of components such as formaldehyde and carbon monoxide that can be particularly hazardous in the close operating conditions of the submarine.